Unloading valve



July 7, 1953 INVENTOR e rfa/A904 5mm ATTORNEYS UNLoanmc vnu;

R. sTl-:vENsoN UNLOADING VALVE original Filed June' 27,1944

A L* why vulve lI-RUYII Ressued July 7, 1953 UNLOADING VALVE RobertStevenson, East Greenwich, R. I., assgnor to Merit Engineering, Inc., aYcorporation of Rhode Island Original No. 2,545,712, dated March 20,1951, Se-

rial No. 542,411, June 27, 1944. Application for reissue March 18, 1953,Serial No. 343,273

Matter enclosed in heavy brackets appears in the original patent butforms no part of this 11 Claims.

reissue specication;

AThis invention relates to an unloading Valve for use in a system inwhich the uid pressure may be maintained without constant action of thefluid pump.

One of the objects of this invention is to provide .a valve throughwhich fluid may pass to supply pressure for transfer of the fluid andyet short circuit the duid flow back to the reservoir whereby the energyrequired by the pump will be relieved.

lAnother object of this invention is to provide a valve in which thefluid passing through the valve will automatically short circuit when apredetermined pressure is reached and thereby relieve the pump whichoperates on the Valve from the work which it has to do when this shortcircuiting arrangement is not cut in.

- Another object of this invention is to provide a quick operating valveand consequently one in which the control of the system may be closelyobtained.

Another object of the invention is to provide no sliding packing whichis exposed to the high pressure fluid when the valve is in unloadingposition and it is desired to maintain the system at high pressurewithout subjecting the pump to high working conditions.

Another object of the invention is to provide two rigid seats for thevalve against which the high pressure works.

Another object of this invention is to p-rovide an arrangement wherebythe Valve may be easily and quickly adjusted.

Another object of this invention is to provide a cartridge which may beremoved from the valve without disconnecting the valve from itscommunicating conduits.

Another object of this invention is to provide a removable cartridgewhich may be. preadjusted and merely insert it into the valve for apredetermined value of operation of the valve or which may beinterchanged with another cartridge for a change of such predeterminedadjustment.

With these and other objects in View, the invention consists of certainnovel features of construction, as will be more fully described andparticularly pointed out in the appended claims.

1n the accompanying drawings:

.. Fig. 1 is a sectional view through the valve;

Fig. 2 is a sectional view through a removable unit which may beinserted in the valve body; and

Fig. 3 is a diagrammatic view illustrating a systemv employing theunloading valve.

i yIn proceeding with this invention I provide a matter printed initalics indicates the additions made by reissue.

valve body which has a port to connect with a high pressure supply and aport to connect with the work with a passageway between these ports. Alow pressure .port is also provided in the valve with a conduitconnecting with a passageway for the high pressure fluid. Thesepassageways are controlled by a main valve with a check valve therein byan-arrangement such that the high pressure will press upon opposite endsof the valve, the surfaces of said valve which are exposed to thepressure being of such relative diameters that the unbalanced pressuredue to the differential of the diameters determines the direction inwhich the valve will be moved. A spring supplements the larger diameterand the pressure on this larger diameter is so controlled that whenpressure is permitted upon this larger diameter the valve will be closedbut when the control acts to remove this pressure on this largerdiameter then the pressure on the smaller diameter will overcome thespringend cause the valve to open. This control is by a predeterminedarrangement so that automatic operation will be had, the arrangementbeing such that the main valve will open at a predetermined highpressure and will close at a predetermined lower pressure. When the mainvalve is open iluid pressure may short circuit to the low pressure portwithout being spring opposed and less work need be done by the meanswhich supply the fluid to the high pressure port and also there is novalve vibration.

A system in which the valve is used is illustrated in Fig. 3 wherein areservoir shown from which a pump takes liquid fo-r supplying it to acylinder A at either end of the cylinder by reason of the four-way valveB. An accumulator may be in the line for maintaining a somewhat equalpressure. As the fluid is supplied at one end of the cylinder to movethe piston therein, fluid is extracted from the opposite end of thecylinder and returned to the reservoir. My unloading valve Ill islocated in this line between the pump and the work in the locationillustrated in this gure and a return line C is provided from anotherport of the valve to the reservoir. One port 20 of the valve isconnected to the pump by conduit E, a second port I8 is connected to thework by conduit D and another port 23 is connected by the return line Cto the reservoir. The supply from conduit E will be directed to eitherconduit C or D. In oper-ation We may assume that it is desired tomaintain from 800 pounds to 1000 pounds pressure for the work required.This pressure is only needed when there is an actual movement of thepiston in the cylinder. Consequently when no movement occurs thepressure rapidly builds up. When this pressure builds'up to 1000 poundsmy unloading valve will automatically operate so asv to switch thecirculation from the work to the by-pass through conduit C back to thereservoir,v -thus reducing the load on the pump considerably.

With reference to the drawings, II) designates a valve body formed of ablock of metal which has a main bore II for the main valve threaded asat I2 and enlarged as at I3 at one end while more restricted portions I4and I6 provide shoulders I5 and I1. The portion vlli of this boreprovides a port I8 for a high pressure discharge which may be threadedas at I9 for connection of some suitable `conduit `such as D leading tothe work. The bodymay have an outwardly projecting boss 22 in which apressure supply port is located which is provided with internal threads2I for connection to some suitable conduit E to the pump and whichcommunicates with the bore I I. provided in this boss having threads 24for connection to some suitable conduit C returning to f.

the reservoir. main bore II.

A smaller bore 25 is also provided in the body I6, the axis ofvwhich isparallel to the bore II. This bore is-of the same size throughout `itsextent fromV one end of the body to the other and receives the-completeunit designated generally 26 and shown by itself in Fig. 2 in this borewhich will be more fully hereinafter described. The bore '25 connectswith the main bore through a passage 21 adjacent one end and through apassage 28 adjacent the other end of the valve body. f

- In the main valve bore II, I position a block This port also connectswith the 30 of generally tubular formation [which at its end 3l] andhaving a portion of the bore thereof reduced as at 30. The end 31 of theblock engages the shoulder I1, while a soft packing 32 serves to sealthis end of the block in the bore Il. A plurality of openings 33extending laterally of the block communicate with the annular chamber 34formed by the reducedportion of the block between itself and the bore Ilat a location so that this annular chamber communicates with the highpressure port 26 and the bore Y30. A suitable soft packing 35 serves toseal the block with the bore II on the opposite side of this annularchamber 34.V A valve seat 36 is provided at one end of the reduced boreV30" against v which the main valve is seated to close communicationbetween the supply port and the return port. A valve seat 36 is providedat the other end of the bore 30. The bore of larger diameter of thisblock [at the junction of the inner surface of the bore and againstwhich the main valve is seated. The inner surface at the opposite endof'fthis'blockj'designated 31 provides a sliding guide for one end ofthevalve.

' A sleeve 38 has threaded engagement with the threads I2 of bore II anditsend engages the block 36 so as to maintain thisv block firmly againstthe vshoulder' I1 rigidly in place in the valve body. The sleeve has aninternal bore 3B of a size substantially larger in diameter than thediameter of the valve seat 36 and infthis bore is located the main valve40. Themain valve 40 .has a tapered surface 4I to engage the valve seat36 and a flange 42 to slidingly engage the `bore 39 of the sleeve 38. Asoft packing v43 is provided to prevent the escape of A low pressureport 23 is also 4 fluid between these engaging surfaces. The valve isalso provided with an end portion 44 slidingly engaging the surface 31of the block 30 and connected to the reduced end of the valve by a stud45 extending axially through the valve and secured by nut and check nut46 and 41. This end v'portion 44 has a surface area normally exposed thebore 25.

to the supply pressure in the bore 37 which is connected to the supply20 through the smaller bore 30 which providesa` valve seat 36' withwhich thev end portion 44 engages when the main valve 40 is 017 its seat41. When the main valve is closed on the seat 41 the effective area ofthe end portion, 44 is balanced. The valve is provided With a centralrecess 48 for the reception of a coil spring 49 which acts to force thevalve toward its seat`41 by engagementwith the abutment surface 49 ofthe plug 56;y

VThis plug 50 is threaded as at 5I into the end of the sleeve 38. Thehollow interior of the reduced portion of this plug connects withtheannular chamber 52 between the head of the plug and the end of thesleeve by reason of a plurality of openings 53 extending through thestem of the plug. This annular chamber 52 is in communication with theconduit 28 so that liquid may be supplied through this passage 28 to thechamber 54 on the enlarged end of the valve.

A suitable soft packing seal 55 is provided in the sleeve at one side ofthe annular chamber k52 and a softpacking 56'is provided in the plug onthe other side of the annular chamber 52 to prevent the escape 'of rthehigh pressure fluid along these surfaces. Y

The unit 25 which is inserted in the bore comprises a sleeve 60 of asize to slide within the bore 25. The sleeve is reduced in diameter atcertain points along its extent as at 6I so as to provide an annularchamber 62 between it and Openings 63 from this chamber62 communicatewith the bore 64 and bore 65 in the sleeve, which latter bore is incommunication with the longitudinally extending channel or recess 66which in'turn communicates through opening 61 with the annular chamber68 surrounding the sleeve 38 which is in communication with the lowpressure port 23 and also the surface of the valve between the valveseat and the head or flange 42. Another recess 10 in this sleevecommunicates with the bore 65 through the conduit 1I and through port 12with the space about the plug 13 and thence through the central channel14 with the annular chamber 15, through openings 16', which annularchamber 15 is in connection with the conduit 2B and the chamber 52.

The upper end of the bore 65 provides a valve seat 16 against which theinclined surface '11 of a valve 18 may engage to close this bore 65. Theflared end 13 of the valve engages 'the borel 64 and isguided along thissurface. Openings through this flared portion of the valve serve forfree communication of the high pressure fluid to the inner conicalsurface of this flared portion and serve to` balance all portions ofthis `end of the valve except the diameter which engages the valve seat.The valve immediately below the valve seat is of reduced diameter but ata point below conduit 1I the valvehas a portion 8| slidingly engagingthe bore 65. The end of the valve is reduced as at 82 and` 83 to projectthrough an opening 84 in a wall which extends laterally across the.sleeve. This opening84 serves as a passage for fluid to the recess. 66and is closed by a ball 85 which is pressed by the plunger 13 to seatingposition through means of a coil spring 86 having one end engaging theabutment 81 threaded as at 88 for movement longitudinally of the bore99.

The sleeve 60 is internally threaded at its opposite ends as at 90 and9| into which plugs 92 and 93 may threadingly engage. The heads of theseplugs are sealed by soft p-ackings 94 and 95 which are located beneaththe heads of these plugs and the ends of the sleeves 60. These closureplugs also serve to abuttingly engage the outer end of the body l0 wherethe bore 25 emerges to the end surfaces. Slots 96 in these plugs serveto assist in turning them into position While an opening 91 may be usedfor wiring to the opening 98 in the ange of the closure 50 so to preventrelative turning of these parts with reference to each other and to thebody.

The guided end portion of the main valve is provided with a check valve|06 which is forced to its seat by a spring |0| abutting the perforatedplate |02 secured in the end of the main valve. Pressure is communicatedfrom. the inlet high pressure port I8, also by reason of the conduits21, 65,1I, 10,12,14, 16, 15, 28, 52, 53 and 54, high pressure istransferred from one end of the main valve 40 on one side of the valveseat 36 to the other end of the valve at the other side of the valveseat 36. The diameter of the valve head 42 at one end of the valvedetermines the closing pressure which Will be applied on the valve whichis assisted by the sp-ring 49. Pressure exerted tending to open thisvalve presses on an area of the valve equal to the diameter of the seat36. The remainder of this end of the valve is all in balanced relation.A complete balance may be provided using pressure of spring 46 alone forclosing.

It is so arranged that if the pressure on the area. 42 of the valve iscut off, then the pressure on the opposite end of the valve willovercome the pressure of the spring 49. and open the valve. The checkvalve |00 prevents pressure from the line D escaping to the return C.The automatic cut-off of the pressure on the area 42 is provided by thepilot valve in the bore and which is a separate unit as shown in Fig. 2.

The ball 85 normally closes the opening 84 and at the same time thespring which forces this ball to its seat also forces the valve 18 fromits seat 16 so that it is normally open.

When the ball 85 is seated, the surface area `thereof exposed to highpressure liquid is such as to provide an unbalanced force acting on theball in a direction tending to move the same towards its seat. Thesurface area of the ball exposed to this force is an area equal to thearea of the opening 84. The spring 86 supplements this force. Thesurface area of the valve 18 subjected to pressures tendingto slidablymove the same toward or from its seat is balanced such that theeffective area thereon exposed to pressure tending to move the same toits seat, when the ball 85 is seated, is an area equal to the area ofthe bore 65 minus the area of the opening 84.

The adjustment of the spring 86 is such that it will yield when thepressure reaches top limit of the range. This may be assumed to be 1,000pounds. Such pressure on the valve 18 will move the same to its seatagainst opposing pressure on the ball 85 and resistance of spring 86.With the ball valve 85 removed from its seat, fluid will escape throughopening 84 and will reduce the pressure opposing the valve 18. l Withthe valve 1|8 seated, the surface area exposed to pressures 6l' tendingto oppose moving the same from its seat is equal to the total area ofthe bore65 and will maintain the valve closed against the action ofspring 86.

When the ball is forced from its closed position liquid may escapethrough the opening 841 to the recess 66, thence through the opening 61through the annular chamber 68, and thence to the port 23 and 10Wpressure side of the valve. The closure of the valve at 18 prevents highpressure fluid from being sup-plied to chamber 54 and area 42 of thehead of the valve. Thus, by the absence of this pressure the main valvewill open and the incoming fluid from conduit E` will pass from the port26 past the valve seat 36 to the port 23 and through conduit C back tothe reservoir and this conditio-n will occur until the pressure inthevvork line drops to an extent, say S00 pounds, when the spring 86will overcome this pressure, open the valve 11, close valve 85, [andopen the pilot Valve] and permit liquid to be supplied to the chamber 54under the higher pressure and consequently press upon this largerdiameter of the valve at this end to close the same. Thus the openingpressure and the closing pressure are in- 'versely proportional to theopening area and closing area.

Upon movement of main 'value 40 from the salue seat 36 the taperedsurface 44 will move to engage value seat 36, the balanced condition onportion 44 is changed. The larger bore 37 is` now shut o l from thesupply pressure, leaving only the diameter of the bore 30', whichprovides the value seat which thetapered surface 44 engages, exposed tothe supply pressure. Thus, the digerence between the diameters of thelarger bore 37 and the smaller bore 30 is at once subtracted from theeectiue pressure on the portion 44, tending to move the value 40upwardly or toward closed position. Further, the pressure upon the valve40 in the diameter of the bore 39 is subjected to the supply pressure.This supply pressure, however, may decrease materially leaving thedischarged pressure acting through the diameter of the bore'37 upon theend portion 44, tending to hold the main value 40 ojf its seat or inopen position and which is opposed only by the spring 49. A free flowfrom port 21 to port 23 will be had even gt low pump pressures withoutany ualueoibraion. l

A relief valve |05 may be placed in the line El With a return connectionF to the reservoir.

I claim:

1. In an unloading valve having a body pro--A vided with a supply port,a discharge port and a return port communicating with the supply port, amain valve normally seated to close communication between said supplyport and return port and subjected on one side thereof to the pressureat the supply port tending to unseat said valve and on the other side tothe pressure at the discharge port tending to seat said valve, a checkvalve between the supply and discharge ports for blocking the return ofHuid from said discharge port Vso proportioned with reference to themain valve'as to area and spring pressure as to bel unseated when saidmain valve is seated and seated when said main valve is unseated, anormally unseated second valve for controlling the said iiuid pressurefrom said discharge port which acts on said main valve, said secondvalve being lsubjected on one side to the pressure at the discharge porttendingto seat said second valve'` to cutoff said pressure from saiddischarge port .7` which acts on said main valve, a vent conduit. insaid body communicating with said return port for draining upon theseating of said second valve the said pressure from said discharge portwhich acts on said main valve for creating a differential pressurecondition across said main valve to unseat the same in response to thesaid pressure from the supply port which acts thereon, a third valve forcontrolling said vent conduit arranged to be normally seated andsubjected on one side to the pressure at the discharge port tending tomove the same to closed position and engaged on the other side by saidsecond Valve to be unseated thereby upon seating of said second valveand a spring supplementing the said fluid pressure acting on said thirdvalve to oppose closing of said second valve and adjustable means topredetermine the fluid pressure range at which said second valve will beseated or unseated.

2. In an unloading valve, a supply port, a discharge port, a passage forfluid between said ports, a return port communicating with the supplyport, a conduit therefrom to said passage v providing a valve seat,amain valve arranged to be normally seated on said seat and subjected onone side thereof to the pressure at the supply port tending to unseatsaid main valve and on the other side to the pressure at the dischargeport tending to seat said valve, a check valve between the supply anddischarge ports for blocking the return of fluid from said dischargeport so proportioned with reference to the main valve as to area andspring pressure as to be normally unseated when said main valve isseated and seated when said main valve is unseated, a second conduit forsupplying fluid from the discharge port to said main valve, a secondvalve in said second conduit normally unseated and subjected on one sidethereof to the fluid pressure in said second conduit tending to seat thesame Yto close said second conduit to cut off the fluid from saiddischarge port to said main valve, a vent conduit from said secondconduit to said return port to drain fluid from said second conduit uponseating of said second valve to create a differential pressure conditionacross said main valve to unseat the same in response to the saidpressure from the supply port which acts thereon, a third valve forcontrolling said vent conduit arranged to be normally seated to closesaid vent conduit and subjected on one side thereof to the fluidpressure in said second conduit tending to seat said third valve andengaged on the other side by said second valve to be unseated therebyupon seating of said second valve, and a spring supplementing the said`fluid pressure which acts on said third valve to oppose the seating ofsaid second Valve and adjustable to predetermine the fluid pressurerange at which said second valve will be seated and said third valveopened.

3. In an unloading valve, a supply port, a discharge port, a passage forfluid between said prtsa return port communicating with the supply port,a conduit therefrom to said passage providing a valve seat, a main valvearranged to be normally seated on said seat and subjected on the highpressure side of said seat to the pressure at the supply port tending tounseat said valve and on the low pressure side of said seat to thepressure at the discharge port tending to seat said main valve, a checkvalve in said main valve located between the supply and discharge portsfor blocking the return of fluid from said discharge port sorproportioned with reference to the main valve as to area and springpressure as to be seated when said main valve is unseated and unseatedwhen said main valve is seated, a spring on the low pressure side ofsaid seat urging said main valve to seated position, a second conduitfrom said passage to supply fluid from the said discharge port to saidmain valve, a second valve in said second conduit normally unseated andsubjected on one side thereof to the fluid pressure in said secondconduit tending to seat said second valve to close said second conduitto cut oi the uid from said discharge port to said main valve, a ventconduit from said second conduit to said return port to drain fluid fromsaid second conduit upon seating of said second valve to create adifferential pressure across said main valve to unseat the same inresponse to the said pressure from the supply port which acts thereon, athird valve for controlling said vent conduit arranged to be normallyseated and engaged on one side thereof by said second valve and unseatedthereby upon the seating of said second valve, said third valve beingsubjected on the other side thereof to the fluid pressure in said secondconduit tending to seat the same and oppose seating of said secondvalve, spring pressure urging said third valve to seated position andadjustable to predetermine the pressure range at which said second valvewill be seated and said third valve unseated.

4. In an unloading valve, a supply port, adischarge port, a passageV`for fluid between said ports, a return port communicating with thesupply port, a conduit therefrom to said passage providing a Valve seat,a main Valve engaging said seat and arranged to be normally seated andsubjected on the high pressure side of said seat to the pressure at'thesupply port and on the low pressure side of said seat to the pressure atthe discharge port, said valve having a portion thereof slidablyextending into said passage and provided with a bore thereincommunicating with said supply port and said discharge port, a checkValve in said bore between the supply and discharge ports for blockingthe return of fluid from said discharge port so proportioned withreference to the main valve as to area and spring pressure as to beseated when said main valve is unseated and unseated when said mainvalve is seated, a spring on the low pressure side of said seat urgingsaid main valve to seated position, a second conduit from said passageto supply fluid from said discharge port to said main valve, a secondvalve in said second conduit arranged to be normally unseated andsubjected on one side thereof to the fluid pressure in said secondconduit tending to seat the same to close said second conduit to cut offthe fluid from said discharge port to said main valve, a ventconduitfrom said second conduit to said return port to drain fluid from saidsecond conduit upon seating of said second valve to create adifferential pressure across said main Valve to unseat the same inresponse to the said pressure at the supply port which acts thereon, athird valve for controlling said vent conduit arranged to be normallyseated and engaged on one side thereof by said second valve and unseatedthereby upon the seating of said second valve and subjected on the otherside thereof to fluid pressure in said second conduit tending to seatsaid third valve to oppose seating of said second valve, spring pressureurging said third valve to seated position and adjustable topredetermine the preslsure range at which said second valve will be seatto the pressure at the supply port and on the low pressure side of saidseat to the pressure at thedischarge port, said valve having a portionthereof slidably extending into said passage and provided with a boretherein communicating with said supply port and said discharge port, acheck "valve in said bore between the supply and discharge ports forblocking the return of fluid from said discharge port so proportionedwith reference to the main valve as to area and spring pressure as to beseated when said main valve is unseated and unseated when said mainvalve is seated, said portion having an abutment thereon and a springacting between said abutment and said check valve urging said checkvalve to seated position, a spring on the low pressure side of said seaturging said main valve to seated position, a second conduit from saidpassage to supply fluid from said discharge port to said main valve, asecond valve in said second conduit arranged to be normally unseated and:subjected on one side thereof to the iiuid pressure in said secondconduit tending to seat the same to close said second conduit to cutoifthe fluid from said discharge port to said main valve,

a vent conduit fromvsaid second conduit to said -return port to drainfluid from said second conduit upon seating of said second valve tocreate a differential pressure across said main valve to unseat the samein response to the said pressure at the supply port which acts thereon,a third valve for controlling said vent conduit arranged to benormally'seated and engaged on one side thereof by said second valve andunseated thereby upon the seating said second conduit tending to seatsaid third valve to oppose seating of said second valve, spring pressureurging said third valve to seated position and adjustable topredetermine the pressure range at which said second valve kwill be sureat the discharge port tending to seat said valve, a check valve betweenthe supply and discharge ports for blocking the return of fluid fromsaid discharge port so proportioned with reference to the main valve asto area and spring pressure as to be unseated when said main valve isseated and seated when said main valve is unseated, a conduit in saidbody for supplying fluid from said discharge port to said main valve,

4a vent conduit from said conduit to said low pressure port, a valveunit in said conduit including a sleeve provided with passages thereincommunicating with said discharge port, main valve and said ventconduit, a second valve in said unit arranged to be normally unseatedand subjected on one side thereof to the fluid presof said second valveand subjected on the other side to fluid pressure in sure in saidconduit tending toseat said second valve to close said passages to cutolf fluid from said discharge port to said main valve, a ball valve insaid unit arranged to be normally seated to control the said ventconduit and subjected on one side thereof to the fluid pressure in saidconduit tending to seat the same and engaged on the other side thereofby said second valve to be unseated thereby upon the seating vof saidsecond valve to drain fluid in said conduit from said main valve tocreate a dierential pressure lacross the main valve to unseat the samein response to the said pressure at the supply port which acts thereon,and a springlurging said ball valve to seated position land opposeseating of said second valve and adjustable to predetermine the pressurerange at whichl said second valve will be seated or unseated.

7.v In an unloading valve, a supply port, a return port, a conduitbetween said ports providing a main valve seat therealong, a dischargeport, a second conduit between said supply port and discharge portproviding a second valve seat therealong, a member having closure forsaid main valve seat andv presenting a diameter greater than thediameter of said main valve seat on the return port side of the seat andsubjected to the discharge port pressure urging the member to cause themain valve to seat, and said member having a second closure for saidsecond valve seat and presenting a diameter greater than the diameter ofsaid second valve seat on the discharge side of the sea't and subjectedto the discharge port pressure urging the member to the second valveseat 'when in engagement therewith, a spring urging said member tonormally engage the main valve seat and open the sec'- ond valve seat,second valve means for control-v ling the pressure at the discharge portacting on the return portside of said member for creating a differentialpressure condition across said member to unseat the same in response tothe pressure at the discharge port acting on said member on the returnport side thereof and seating said second closure on said second valveseat, whereby the difference in diameter of the second valve seat andthe greater diameter on the discharge port side thereof is subtractedfrom the area subjected to the supply port' pressure.

8. In an unloading valve, a supply port, a discharge port and a returnport, a main valve normally seated to close communication between saidsupply port and returnport and subjected on thelow pressure side thereofto the pressure at the discharge port tending toseat said valve `andsubjected at the other side thereof tothe 'pressure at A'the supply porttending to' unseat 'said valve, a spring'urging said valve to seatedposition, said valve having additional opposite surfafce area-s thereonexposed to the pressures'at the supply port and discharge port in abalanced condition when said main valve is seated, second valve meansfor controlling the pressure at the discharge port acting on the saidone side of said main valve for creating a differential pressurecondition across said main valve to unseat the same in response to thepressure at the supiply port, and other valve means for shutting 01T thepressure at the supply port acting on one of said opposite areas uponthe unseatino of said main valve whereby the pressure at the dischargeport will act on said other of said opposite areas of the main valve tomaintain the same unseated to be opposed only by the pressure of saidspring.

9. In an unloading valve, a supply port, a discharge port and a returnport, a main valve normally seated to close communication between saidsupply port and return port and having a, bore therethrough for thepassage of fluid from said supply port to said discharge port, a checkvalve for blocking the return of fluid from said discharge port throughsaid bore and arranged to be unseated when said main valve is seated andseated when said main valve is unseated, said main valve being subjectedon the low pressure side thereof to the pressure at the discharge porttending to seat said valve and subjected on the high pressure sidethereof to the pressure at the discharge port tending to seat said valveand subjected on the high pressure side thereof to the pressure at thesupply port tending to unseat said valve, a spring urging said valve toseated position, said valve having additional opposite surface areasthere on exposed to the pressures at the supply port and discharge portin a balanced condition when said main valve is seated, second valvemeans for controlling the pressure at the discharge port acting on thesaid one side of said main valve for creating a dierential pressurecondition across saidmain valve to unseat the same in response to thepressure at the supply port, and other valve means for shutting o1? thepressure at the supply port acting on one of said areas upon theunseating of said mainvalve whereby the pressure at the discharge portwill act on said other of said areas on the main valve to maintain thesame unseated and to be opposed only by the pressure of said spring.

10. In an unloading valve, a supply port, a discharge port and a returnport, a main valve normally seated to close communication between saidsupply port and return port and subjected on one side thereof to thepressure at the supply yport tending to unseat said valve and subjectedon the other side thereof tothe pressure at the discharge port tendingto seat said valve, a second valve for controlling the pressure at theAdischarge port acting on the said main valve, said second valve beingsubjected on one side to the pressure kat the discharge port tending toseat said second valve to cut off said pressure from said discharge portwhich acts on the said main valve, avent conduit for draining upon theseating of said second valve the pressure at said discharge port actingon the said main valve for creating a differential pressure conditionthereacross to unseat the same in response to pressure at the vsupplyport, a third valve for controlling said vent conduit arranged to benormally seated and subjected on one side to pressure at the dischargeport tending to seat the same and engaged on the other side thereof byvsaid second valve to be lilil unseated thereby upon seating of saidsecond valve and a spring supplementing the said fluid pressure actingon said third valve to oppose closing of said second valve whereby uponunseating of said third valve said pressure at the discharge porttending to seat said second valve will be opposed only by the pressureof said spring.

11. In an unloading valve, a supply port, a discharge port and a returnport, a main valve normally seated to close communication between saidsupply port and return port and subjected on the high pressure sidethereof to the pressure at `the supply port tending to unseat said valveand subjected on the low pressure side thereof to the pressure at thedischarge port vtending to seat said valve, means including a secondVvalve for'controlling the said fluid pressure tending to vseat saidvalve, a conduit to each side of said second valve'for the flow of fluidunder pressure therethrough, said second valve ccntrolling'said conduitand subjected onY one side thereof to pressure in said conduit -tendingto move saidsecond valve to shut of 'the fiow of fluid through saidconduit, a vent conduit from said conduit for draining the same upon theseating of said second valve, a third valve for controlling saidv ventconduit arranged to be normally seated andsubjected on one side to thepressurey in said conduit tending to seat said third valve and engagedon the other side thereofbysaid second'valve to Vbe unseated therebyupon seating of said' second valve and a spring supplementing the saidpressure acting `on said third valve to oppose closing said secondvalve, said fluid pressure acting on said second valve tending to seatthe same will be opposed only by the pressure of said spring.

ROBERT STEVENSON.

References'Cited in the ie of this patent Vorthe OriginaI'patenIt UNITEDSTATES PATENTS Number Name p Date 2,091,596 Kuppel Aug. 3l, 19372,188,463 v Mercier Jan. 30, 1940 2,241,665 Herman May 13, 19412,264,375 Hill Dec. 2, 1941 2,279,571 Kane Apr. 14, 1941 2,312,877Campbell Mar. 2, 1943 2,327,942 Thoresen Aug. 24, 1943 2,404,102 SchultzJuly 16, 1946 2,410,751 Schultz Nov. 5, 1946 2,447,820 Schultzl Aug. 24,1948 2,545,712 Stevenson Mar. 20, 1951 FOREIGN PATENTS Number CountryDate 8,799 Great Britain May 3, 1895 267,978 Great Britain June 23,192'? 587,769 Great Britain Aug. 31. 1932

